How to get rid of imperfections after applying subsurf?
I managed to solve it! 

I deleted the vertical edge loop (Alt + RMB) then X &rarr; Edge Loop
Then Ctrl + R to make another vertical loop cut and I was more careful not to slide it as far.

This is how it looks now



This is how it looks in the edit mode with the new edge loop



I don't know if it's the right thing to do but it worked for me!